The present invention relates to a drive control system for sensor-less motor and more specifically to the technique which may effectively be applied to the drive control of a brush-less DC multi-phase motor not including a rotation detecting sensor, for example, the technique which can be effectively applied to the drive control of a spindle motor for high speed drive of a disk storage medium (platter) of a HDD (hard disk drive).
The HDD reads or writes information with the seeking and following operations of a magnetic head on a recording surface formed on the surface of platter while the disk type magnetic recording medium called the platter is rotated at a high speed. In order to realize high speed read/write operations of information in this HDD, the rotating speed of platter must be increased.
The platter is driven to rotate with a spindle motor. For this spindle motor, a sensor-less motor is generally used. This sensor-less motor is a brush-less DC multi-phase motor not including a rotation detecting sensor. This motor is suitable, for example, for high speed rotation of a disk type recording medium such as a platter.
The sensor-less motor, can form an effective structure of the motor and drive system thereof since an independent rotation sensor is not used to detect the magnetic pole position of a rotor. Instead, the magnetic pole position of rotor must be detected without use of the sensor. Therefore, the magnetic pole position of rotor is detected, in the sensor-less motor of this type, by utilizing B-EMF (Back Electromagnetic Force) induced on a field coil. B-EMF is a voltage induced on the field coil through the rotation of a rotor. Therefore, when the rotor is in the rotating condition, the magnetic pole position of rotor and rotating speed can be detected by utilizing its B-EMF.
In the case where this sensor-less motor is used as the spindle motor, the motor is driven to rotate with an open loop control and is sequentially subjected to the commutation control and PLL (phase lock loop) control based on the back electromotive force of the field coil in view of holding the motor in the predetermined steady rotating speed condition. The sequence control up to the steady operation from this drive can be conducted with an LSI (semiconductor integrated circuit) system.
However, the inventors of the present invention have found the technique explained above has following problems.
In other words, in the drive control of a sensor-less motor explained above, the drive control in the steady rotating condition can be realized rather easily with the commutation and PLL controls based on the back electromotive force of field coil, but detection of rotation with the back electromotive force cannot be utilized during the transitional condition until the steady rotating condition is started, particularly immediately after the drive. Therefore, the drive control at the time of starting the motor is executed with the open loop control and when the rotation reaches a certain rotating speed with the open loop control, such open loop control is shifted to the communication and PLL controls. However, since the open loop control is a kind of estimated control method and the estimated operation cannot always be attained. In the prior art, it has been inevitable that a fault is generated at the beginning of drive with a certain probability.
In the sensor-less motor not including a rotation sensor, if a drive mistake occurs, it is difficult to accurately detect such mistake. A drive mistake occurs when the estimated operations are not carried out with a certain reason. Therefore, if a drive error occurs, detection of such drive mistake is not executed as estimated with a considerable probability. In this case, various problems such that recovery from the drive error and re-drive are delayed or the motor is stacked in the non-driven condition may be generated.
Moreover, a problem that shift to the steady operation from drive is not carried out smoothly and the sequence to shift to the drive control of steady operation is executed even when the drive fails has been generated easily.
When the motor is driven successfully and the drive control is shifted to the PLL control, the phase lock of the PLL control is unlocked in a certain case, for example, when a load of motor changes to a large extent. In this case, the motor is stepped out or stops in the worst case. The motor of this type is driven with the PWM-controlled current but when the motor is stepped out, a regeneration current in the PWM drive is returned to the power supply and thereby the power supply voltage rises irregularly, resulting in the possibility of breakdown of the drive circuit.
Loss of synchronization (step-out) due to the unlock of PLL is also generated in some cases when the PWM duty becomes 100% due to reduction of voltage and over-load condition. A spindle motor is subjected to the soft-switch drive or sine-wave drive for smoothly changing over the power feeding phase. In this case, when the PWM duty reaches 100%, a current of the non-power feeding phase cannot be perfectly reduced to zero at the timing near the timing for detecting zero-cross of B-EMF and thereby a kick-back is generated in the drive voltage. Therefore, when the rotating position of rotor is detected with the zero-cross phase of B-EMF, such kick-back prevents accurate detection of the zero-cross phase and thereby such detection error becomes large and PLL is unlocked.
The first object of the present invention is to provide technique for accurately and quickly driving the sensor-less motor.
The second object of the present invention is to provide the technique for accurately monitoring the conditions of the sensor-less motor at the time of drive in order to quickly drive the sensor-less motor with higher reliability.
The third object of the present invention is to provide the technique for quickly realize recovery from a drive mistake and re-drive of motor even when a drive mistake occurs in the sensor-less motor.
The fourth object of the present invention is to provide the technique for quickly realize recovery from a fault condition by accurately detecting unlock of the PLL when the sensor-less motor is successfully driven and shifted to the PLL control condition.
The fifth object of the present invention is to provide the technique for accurately detecting the rotating position of rotor with zero-cross of B-EMF.
The aforementioned and the other objects and features of the present invention will become apparent from the following explanation of this specification to be made with reference to the accompanying drawings.
The typical inventions of the present invention disclosed in this specification can be explained briefly as follows.
The present invention discloses a drive control system for sensor-less motor in which the motor is driven to rotate by switching a current of a field coil in each phase of a multi-phase sensor-less motor depending on the rotation phase of motor and the drive control thereof is subjected to the PLL control. Moreover, immediately after the drive of motor, a desired phase is selected as the detection phase, a voltage induced on the coil of the detection phase when the power is fed only for a short period of time to the field coil in the phase other than the detection phase and the magnetic pole position of rotor is detected from the amplitude condition of the induced voltage detected. Based on this detection, the power feeding phase of motor drive is determined and the power feeding to drive the motor is conducted depending on such determination. The detection of magnetic pole position and the power feeding to drive the motor are conducted alternately. Accordingly, drive of sensor-less motor can be realized accurately and quickly.